1. Field of the Invention
The present invention relates to a light-emitting system. More particularly, it relates to improvement in a light-transmissible layer of a light-emitting system using a Group III nitride compound light-emitting device (hereinafter merely referred to as xe2x80x9clight-emitting devicexe2x80x9d) such as an LED as a light source.
The present application is based on Japanese Patent Application No. 2000-2748, which is incorporated herein by reference.
2. Description of the Related Art
In a general light-emitting system, an LED is mounted on a cup portion of a mount lead and connected to an inner lead through an electrically conductive wire, as described in JP-A-59-54277. The LED, together with the electrically conductive wire, a part of the mount lead and a part of the inner lead, is covered with a sealing member made of a light-transmissible resin. Such a configuration is employed in an LED made of Group III nitride compound semiconductors. For example, see Japanese Patent No. 2927279.
In the light-emitting system having such a configuration as described above, the sealing member is generally made of a transparent epoxy resin. JP-A-10-215004 has proposed that an epoxy resin using a curing catalyst for cationic polymerization is used as the sealing member in order to achieve prevention of deformation/destruction; prevention of electrode corrosion; facilitation of assembling; reduction of cost; and so on. The proposal has shown the case where any one of a bisphenol-A type epoxy resin, a bisphenol-F type epoxy resin and an alicyclic epoxy resin is used as the epoxy resin or a combination thereof is used as the epoxy resin.
Because JP-A-10-215004 relates to a light source for an image scanner, it is conceived that the LED to be used in JP-A-10-215004 is constituted by any other materials than the Group III nitride compound semiconductors. Although JP-A-10-215004 has described that an amine type epoxy resin is discolored under environment of use in JP-A-10-215004, it is a matter of common knowledge that weather resistance is worsened when amine is used as a curing catalyst, that is, this phenomenon is not limited when the amine type epoxy resin is used as a member for sealing an LED used as a light source.
Japanese Patent No. 2927279 discloses an epoxy resin as an example of a sealing member.
An epoxy resin is generally used as a member for sealing an LED as described above. However, there has been no specific discussion about what deteriorating phenomenon occurs when the epoxy resin is used as a member for sealing a Group III nitride compound semiconductor light-emitting device which outputs short-wave light.
An object of the present invention is to provide an epoxy resin adapted to a member for sealing a light-emitting device made of Group III nitride compound semiconductors in pursuit of characteristic of the epoxy resin used as the sealing member.
The inventors of the present invention have eagerly examined the relationship between a light-emitting device made of group III nitride compound semiconductors and an epoxy resin. As a result, the inventors have conceived an invention configured as follows. That is, a light-emitting system comprises: a Group III nitride compound semiconductor light-emitting device; and a light-transmissible layer surrounding the light-emitting device, wherein the light-transmissible layer is made of an alicyclic epoxy resin.
The light-emitting device made of Group III nitride compound semiconductors emits light with a short wavelength. Because such light with a short wavelength has high energy, deterioration (yellowing) of the epoxy resin is accelerated. Hence, when the epoxy resin is of an aromatic type, the epoxy resin satisfies physical properties such as curing speed, hardness, etc. of a sealing member but it is difficult to obtain sufficient durability because the double bond of the epoxy resin serves as an active seed so that the epoxy resin is affected by light emitted from the light-emitting device. For example, there is a possibility that a bisphenol-A type epoxy resin is denatured to quinoid (brown) by light. On the other hand, an aliphatic epoxy resin has sufficient durability against light but is unsuitable as a sealing member in terms of physical properties such as remarkably high curing speed, large distortion after curing, etc.
In this respect, an alicyclic epoxy resin is hardly deteriorated (yellowed) even in the case where the alicyclic epoxy resin is disposed in proximity of the Group III nitride compound semiconductor light-emitting device because the alicyclic epoxy resin has no double bond as an active seed. Also from the point of view of physical properties, the alicyclic epoxy resin is used sufficiently as a member for sealing the light-emitting device though the alicyclic epoxy resin does not amount, in physical properties, to the aromatic epoxy resin.
As a result of eager investigation by the inventors of the present invention, it has been found that an epoxy resin composition proposed in JP-A-11-199645 is used preferably as the aforementioned alicyclic epoxy resin. The proposed epoxy resin is a hydrogenated epoxy resin prepared by hydrogenation of an aromatic epoxy resin and having an alicyclic hydrogenating ratio of not lower than 85%, an epoxy group loss ratio of not higher than 20% and a total chlorine content of not larger than 0.3% by weight.
In this paragraph, related matters will be quoted from JP-A-11-199645 in order to clarify the disclosure of the invention.
(1) The present invention relates to an epoxy resin composition containing (A) a hydrogenated epoxy resin prepared by hydrogenation of an aromatic epoxy resin and having an aromatic ring hydrogenating ratio of not lower than 85%, an epoxy group loss ratio of not higher than 20% and a total chlorine content of not larger than 0.3% by weight, and (B) an epoxy resin curing agent.
(2) The present invention relates to the epoxy resin composition according to (1), wherein 0.01 to 200 parts by weight of the epoxy resin curing agent are mixed with 100 parts by weight of the hydrogenated epoxy resin.
(3) The present invention relates to the epoxy resin composition according to (1) or (2), wherein the hydrogenated epoxy resin is a hydrogenated epoxy resin prepared by dissolution of an aromatic epoxy resin in an ether solvent and hydrogenation of the aromatic epoxy resin under pressure and under presence of a catalyst composed of graphite, and rhodium or ruthenium carried by the graphite.
(4) The present invention relates to the epoxy resin composition according to any one of (1) through (3), wherein the hydrogenated epoxy resin is a liquid epoxy resin prepared by hydrogenation of a bisphenol-A type epoxy resin and having a viscosity of not higher than 2.5 Paxc2x7s at 25xc2x0 C. when measured by a rotaviscometer.
(5) The present invention relates to the epoxy resin composition according to any one of (1) through (3), wherein the hydrogenated epoxy resin is an epoxy resin prepared by hydrogenation of a novolac epoxy resin having an epoxy equivalent amount in a range of from 150 to 230 and represented by the following general formula: 
in which each of R1, R2 and R3 shows a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, n shows a numerical value of from 0 to 10, and z shows a hydrogen atom or the formula: 
in which each of R1, R2 and R3 shows a hydrogen atom or an alkyl group having 1 to 4 carbon atoms.
(6) The present invention relates to the epoxy resin composition according to any one of (1) through (5), wherein the hydrogenated epoxy resin has a total chlorine content of not larger than 0.3% by weight and a hydrolytic chlorine content of not larger than 0.1% by weight.
(7) The present invention relates to the epoxy resin composition according to any one of (1) through (6), wherein the epoxy resin curing agent is a compound selected from the group consisting of amines, acid anhydrides, polyhydricphenols, imidazoles, protonates, dicyandiamides, organic acid hydrazides, polymercaptans, and organic phosphines.
(8) The present invention relates to the epoxy resin composition according to any one of (1) through (7), wherein the epoxy resin curing agent has an aromatic ring content of not larger than 10% by weight with respect to the total amount of the curing agent.